Even many backend devs seem to shy away from things like SQL because they're not too comfortable with it. Which isn't bad per se, it's very easy to make a small mistake in a query that crushes the database, just a personal observation of mine.
The idea that there is some rule that you don’t mix languages seems like absolute nonsense. If someone suggested to me that it was _possible_ I’d be extremely curious what wild tradeoffs they were making to get there.
However, in my work I've seen plenty of developers with all manner of interests and experiences align only on one or two languages, and if that's your company's talent pool, single language code bases seem like a good idea.
Of course this skips over all the usage of scripting languages (makefile/bash/Python/XML) which in my experience are seen as quirks of build tooling rather than part of the product.
Considering that they'll want to use Node even to make coffee, I'd argue that statement is wildly inaccurate.
The modern web is a gigantic mess with security features hacked on top of everything to make it even remotely secure and the moment it hit the desktop thanks to electron we had cross site scripting attacks that allowed everyone to read local files from a plugin description page. If anything it is the ultimate proof how bad things can go.
I have used around 20+ in my little project (mostly solo) and I have now:
* Rust
* Kotlin
* Swift
* Html
* Sql with variations for: Postgres, Sqlite, Sql Server, Firebird, DBISAM, MySql
* Go
* FreePascal
And now is when I have less languages.
People are flexible.
